Spring Nested object is getting null while submitting form - spring

Question

I am trying to post data with thymeleaf, command model has two nested objects, one is fetching data, while another is fetching null. I am confused, what is going on behind the scene, though using the same concept and code.
Please notice, I am getting data for People Object in logs, but not for Project Object, though using the same code. Please help.
Form Snippet.
<form th:fragment="form" method="post" th:object="${expense}" th:action="#{/createexpense}">
<input type="hidden" th:field="*{expenseId}" />
<div class="form-group">
<label class="col-md-4 control-label" for="textarea">Expense Description</label>
<div class="col-md-4">
<textarea class="form-control" id="textarea" th:field="*{description}" name="textarea">Expense Description</textarea>
</div>
</div>
<div class="form-group">
<label class="col-md-4 control-label" for="textinput">Amount</label>
<div class="col-md-4">
<input id="textinput" name="textinput" type="text" placeholder="Enter Amount" th:field="*{amount}" class="form-control input-md">
</div>
</div>
<div class="form-group">
<label class="col-md-4 control-label" for="textinput">Project</label>
<div class="col-md-4">
<select class="form-control" id="sel1" th:field="*{project}">
<option th:each="project: ${projects}" th:value="${{project.projectId}}" th:text="${project.name}">1</option>
</select>
</div>
</div>
<div class="form-group">
<label class="col-md-4 control-label" for="textinput">People</label>
<div class="col-md-4">
<select class="form-control" id="sel1" th:field="*{people}" >
<option th:each="people: ${peoples}" th:value="${people.id}" th:text="${people.name}">1</option>
</select>
</div>
</div>
<div class="form-group">
<label class="col-md-4 control-label" for="textinput">Expense Type</label>
<div class="col-md-4">
<select class="form-control" id="sel1" th:field="*{expenseType}">
<option th:each="exp: ${expenseTypes}" th:value="${exp}" th:text="${exp}">1</option>
</select>
</div>
</div>
<div class="form-group">
<label class="col-md-4 control-label" for="textinput">Create
Expense</label>
<div class="col-md-4">
<input type="submit" class="btn btn- danger" value="Submit"/
</div>
</div>
Model Bean Class
#Data
#JsonIgnoreProperties(value = {"createdAt", "updatedAt"},
allowGetters = true)
#Entity
public class Expense {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long expenseId;
#Lob
private String description;
#OneToOne
#Cascade(CascadeType.ALL)
private People people;
private Double amount;
#Temporal(TemporalType.TIMESTAMP)
#CreatedDate
private Date createdAt;
#Temporal(TemporalType.TIMESTAMP)
#LastModifiedDate
private Date updatedAt;
#ManyToOne
#Cascade(CascadeType.ALL)
private Project project;
#Enumerated(EnumType.STRING)
private ExpenseType expenseType;
public Expense(String description, Double expense) {
this.description = description;
this.amount = expense;
}
public Expense() {
}
public void setCreatedAt(Date createdAt) {
this.createdAt = new Date();
}
public Date getUpdatedAt() {
return updatedAt;
}
#PreUpdate
public void setUpdatedAt() {
this.updatedAt = new Date();
}
}
Controller Snippet
#PostMapping(path="/createexpense")
public Expense addExpense(#ModelAttribute("expense") Expense expense ,BindingResult result){
log.debug(expense.toString());
expense.setPeople(peopleService.getPeople(expense.getPeople().getId()));
expense.setProject(flatProjectService.getFlatProjectById(expense.getProject().getProjectId()));
return expenseService.createExpense(expense);
}
#GetMapping(path="/createexpense")
public ModelAndView addExpense(ModelAndView modal){
//adding projects list and people list in expense view
modal.addObject("projects", flatProjectService.getAllProjects());
modal.addObject("peoples", peopleService.getAllPeoples());
modal.setViewName("createexpense");
modal.addObject("expense", new Expense());
modal.addObject("expenseTypes", ExpenseType.values());
return modal;
}
Error Logs
2018-07-22 18:22:44.010 DEBUG 25500 --- [nio-8080-exec-5] c.d.b.controller.HomeController : Expense(expenseId=null, description=hello, people=People(id=2, name=Avinash, peopleType=null, phoneNo=9504974665, address=Beside Maa Clinic, expense=[], createdDate=2009-06-01 13:45:30.0, updatedDate=2009-06-01 13:45:30.0), amount=5000.0, createdAt=null, updatedAt=null, project=null, expenseType=PAID)
2018-07-22 18:22:44.090 ERROR 25500 --- [nio-8080-exec-5] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException: null

Answer 1

Looking at your HTML logic. I suspect issue is in Project Loop
You are defining th:field="*{project}"
but using as pro in option
Ideally it should be like this
<div class="form-group">
<label class="col-md-4 control-label" for="textinput">Project</label>
<div class="col-md-4">
<select class="form-control" id="sel1" th:field="*{project}">
<option th:each="project: ${projects}" th:value="${project.projectId}"
th:text="${pro.name}">1</option>
</select>
</div>
</div>